Filled composition and article containing perfluorinated surfactant

ABSTRACT

1. AN ARTICLE COMPRISING (A) A FLAT BOARD WHICH COMPRISES (1) ABOUT 15 TO ABOUT 70% OF A HARDENED, SYNTHETIC, ORGANIC RESIN; (2) ABOUT 30 TO ABOUT 85% NON-CONDUCTIVE FILLER; AND (3) ABOUT 0.001 TO ABOUT 1.0% OF A SURFACTANT HAVING A PERFLUORINATED CHAIN AT LEAST THREE CARBON ATOMS ALONG AT ONE END AND A POLAR GROUP AT THE OTHER END, SAID SURFACTANT POSSESSING THE PROPERTY OF LOWERING THE SURFACE ENERGY OF SAID RESIN BY FREELY MIGRATING TO THE SURFACE OF SAID RESIN AND TO ITS INTERFACES WITH SAID FILLER AFTER SAID RESIN IS HARDENED; AND (B) A CONDUCTING CIRCUIT BONDED TO AT LEAST ONE SIDE OF SAID FLAT BOARD.

Oct. 15, 1974 FILLED COMPOSITION AND ARTICLE CONTAINING G R. SPRENGLIN G 3,841,957

PERFLUORINATED SURI'ACTART I Filed Oct. 17. 1972 2 Sheets-Sheet l FIG. I

Oct. 15, 1'14 SPRENGLING 3,841,957

. FILLED COMPOSITION AND, ARTICLE CONTAINING PERFLUORINATED sURrAc'rANT Filed Oct. 17, 1972 2 Sheets-Sheet 2 FIG. 2

I I l I I I I I I I Io I0 I03 I04 Io Io I0 Io Io IOIO INSULATION RESISTANCE MEGOHMS FIG. 3

' I l r l I I" I l 'l I Io Io I0 I0 Io I6 I0 .10 I0 IOIO INSULATION RESISTANCE, MEGOHMS' 5 FIG. 4

I I I I l I I l I l I I0 Io O Io I0 I06 I0 Io I0 Io INSULATION RESISTANCE, MEGOHMS FIG. 5

I I I I l I v I l I -I I Io Io I0 Io Io I0 Io II: Io Io' INSULATION RESISTANCE, MEGOHMS United States Patent US. Cl. 161-186 9 Claims ABSTRACT OF THE DISCLOSURE The invention herein described comprises a fiat board comprising a base substrate comprising 1570% of a hardened, synthetic resin, 30 to 85% non-conductive filler, and .001 to 1% of a perfluorinated surfactant. A conductive circuit is bonded to at least one side of said flat board.

BACKGROUND OF THE INVENTION The electrical resistance of almost all filled, resinous, electrical insulating materials decreases when the materials are exposed to high humidity. Depending on the material, the decrease in resistance may be due to conduction across the surface of the material or to conduction through its volume or both. Decreases in surface resistance can be reduced by encapsulating the material in a hydrophobic coating, but this has little effect on volume resistance. The use of silicone coupling agents mixed into the resin or coating the glass of a glass-filled resin with water-repelling compounds such as methyl trichlorosilane or methyl trimethoxysilane also has little effect on volume resistance.

The decrease in volume resistance of glass reinforced resinous materials in high humidity can make it difiicult or impossible to meet design objectives and can cause the failure of the circuit in operation.

RELEVANT ART M. J. Pike in a March 1972 article in Paint and Varnish Production titled, Fluorochemical Surfactants, describes an epoxy resin containing 0.3 percent PO-430," a 3M Co. perfluorinated surfactant.

J. N. Shepard and John P. Ryan, in a January 1956 article in the Journal of Physical Chemistry, volume 60, pages 127 to 128, titled The Use of C-l4 Labeled Perfiuoro-Octanoic Acid in the Study of Adhesion and Other Surface Phenomena, describes the wetting properties of per-fluoro-octanoic acid. That subject is further discussed by Marianne K. Bernett and W. A. Zisman in a November 1959 article in the Journal of Physical Chemistry, volume 63, titled Wetting of Low-Energy Solids by Aque ous Solutions of Highly Fluorinated Acids and Salts.

SUMMARY OF THE INVENTION I have found that the drop in volume resistance of filled, resinous materials which occurs in high humidity is greatly reduced when certain perfluorinated surfactants are present in the material. Ordinarily, volume resistance may drop from ohms to as low as 10 ohms in high humidity. In the boards of this invention internal conduction paths do not appear in high humidity and the volume resistance remains at about the level of a dry board. Also, surface resistance under these conditions remains higher than that of composites not so treated. Since surfactants usually make a surface more easily wetted, one would expect a surfactant to draw moisture into the material and lower its resistance still further. It is, therefore,

quite surprising that the particular surfactants of this invention have the opposite effect. In addition, the surfactants, particularly the surfactants mixed into the resin 3,841,957 Patented Oct. 15, 1974 reduce the drop in surface resistance which occurs in high humidity even though they are not applied to the surface.

Also, normally when glass is coated with a surfactant the surfactant will prevent the resin from wetting the glass and therefore a poor bond is made between the resin and the glass which results in a decrease in flexural strength. However, a decrease in fiexural strength has not been observed when glass is coated with the surfactants of this invention.

The plastic articles of this invention are used for electrical insulators such as in printed circuit boards, terminal boards, etc. The use of the surfactant in the article does not reduce the adhesion of copper to the board, nor does it cause measling after soldering (measling is the formation of opaque areas due to the bond between the resin and the glass breaking).

DESCRIPTION OF THE INVENTION FIG. 1 is an isometric view in section of a portion of a certain presently preferred printed circuit board according to this invention. FIGS. 2, 3, 4, and 5 are graphs explained in Example 1.

In FIG. 1 a printed circuit board 1 is composed of an insulating board 2 with conducting circuits 3 and 4, usually copper, bonded to it on each side. A plated hole 5 in the board 2 connects portions of the two circuits. Electronic component 6 has leads 7 which are thermally bonded to the circuit 3 with solder 8. A coating 9 (too thin to show on drawing) of a fluorine compound covers the board and electronic component.

The insulating board can be made of almost any organic resinous material. Resin as used herein includes hardeners, etc. which are used if the resin is thermosetting. Examples of suitable resins include epoxies, polyesters, nylon, polyimides, polyamide-imides, polysulfones, polyphenylene oxide, polystyrene, polyethers, phenolics, polyolefins such as polyethylene or polypropylene, etc. Epoxies, polyesters, and phenolics are the most Widely used materials but an epoxy such as the diglycidyl ether of bisphenol A is preferred because of its strength, resistance to measling, and other properties desirable in printed circuit boards and other articles. The insulating board may have almost any shape or dimension, but rectangular boards one inch to one foot in length and thickness and 10 to 100 mils thick are typical sizes for use as printed circuit boards.

The resin is filled to form a composition which is about 15 to about 70% (all percentages herein are by weight) resin and about 30 to about inorganic nonconductive filler. A glass-epoxy composition is typically about /3 to /3 glass and the rest epoxy resin, but the amount of glass can be up to 85 in filament-wound materials.

The use of the surfactants of this invention is expected to decrease the power (loss) factor when the filler is in particulate form. However, the more dramatic decrease in the drop in resistance in high humidity occurs when the filler is elongated and this invention is therefore particularly applicable to materials containing elongated fillers. The effect is primarily uni-directional in the direction of the filler when the filler is both elongated and orientated in one or more particular directions. For example, glass roving would produce a primarily unidirectional effect and glass cloth primarily a bi-directional effect. Other examples of suitable fillers include glass mat, asbestos, and silica. Glass is the preferred filler because it is inexpensive, has great strength, and is most subject to improvement by this invention.

The surfactant used in this invention has two ends a perfluorinated chain at least 3 carbon atoms long, at one end and a polar group at the other end. The surfactant is essentially linear although it may have short branches.

It is preferably saturated so that it is more stable to oxidation. The surfactant has the property of lowering the surface energy of the resin in which it is used both when the resin is a liquid and when the resin has solidified. This property is necessary to insure that the surfactant will migrate to the surface of the resin and to the interface of the resin with the filler. A preferred surfactant has the general formula where Y is a polar group, X is H, F, Cl, Br, or a mixture thereof, m+n is an integer from 3 to 18, and m is an integer equal to or greater than 0.2 times 11 (truncating the product). In the formula n+m is preferably an integer from 6 to 12 as smaller surfactants are more volatile and ditficult to use before they evaporate; larger surfactants are not very soluble and as they are less mobile they do not migrate to surfaces within a reasonable time.

If the surfactant is mixed into the resin, Y in the formula is a polar group capable of being chemisor'bed onto the filter being used. Chemisorbed means that the Y groups bond to the filler with sufiicient tenacity so that they are not washed off by water. The chemisorption of the surfactant on the filler prevents water from leeching it out of the material. Suitable chemisorbed Y groups inelude where R is hydrogen or alkyl to C R is alkylene from C to C R is alkyl to C and A is an anion. Chemisorbed surfactants should be mixed into the resin and should not be coated onto the filler in order to be eifective.

If the surfactant is coated onto the filler, Y in the formula is a polar group which resists chemisorption onto the filler. Chemisorption is not desirable in this case because the concentration of the surfactant is generally high enough to form a monolayer which may repel the resin and prevent a good resin-filler bond. Such surfactants are preferable relatively insoluble (i.e., less than 1%) in the resin used because otherwise too much surfactant is dissolved into the resin and too little remains on the glass. Preferred non-chemisorbing groups include -CCOH,

-SO H and salts thereof, where M is H or m 2m n 2n+1 where m, n, and X are as previously defined. Examples include perfluoro butyric acid, CF CF CF COOH, and perfluoro octanoic acid, C F COOH, the latter being preferred as it is less volatile. Other suitable examples include CF3 7803K, (C4 12F9 25C2H4O 2P0 C5F11COOH, C F COOH,

etc.

The surfactant may be coated onto the filler from about a 0.1 to about a solution. Suitable solvents include water and methanol. The solution i applied to the filler by any suitable means although it is preferable to immerse the filter in the solution to insure complete and uniform coverage. The solvent is then evaporated, preferably as quickly as possible to prevent solvent which evaporates first from drawing the solution out of internal spaces which would result in a non-uniform distribution of the surfactant. Alternatively, this problem with evaporation can be avoided by using a solution in a solvent such as, for example, methanol, then leeching the solvent out of the internal spaces by washing with a miscible non-solvent such as hexane, thereby precipitating the surfactant in the internal spaces.

Resin is applied to the filler by immersion, roll coating, or other means known to the art. Solvent, if present, is evaporated and the filler-resin composite is hardened singly or in a stack of composites under up to about 1000 p.s.i. to form a laminate. If the resin is thermoplastic it is melted and is hardened by cooling. If the resin is thermosetting the resin is melted and is hardened by curmg.

Since the amount of surfactant used is quite small and is inexpensive per pound of material produced, it is preferable to both coat the filler with one surfactant and mix another surfactant into the resin to gain as much protection as possible against a decrease in volume resistivity.

In order to further insure against a drop in surface resistivity particularly under flushing conditions it is preferable to coat the finished article with another type of fluorine compound which is described in my copending application of even date, Ser. No. 298,213 titled Printed Circuit Board and Method of Making It, herein incorporated by reference. Briefly, that application describes a monomer of the formula where p is an integer from 2 to 9, q is an integer from 1 to 9, R is H or CH,, R is H, F, C1, or Br, and to of the R atoms are P and 0 to 20% of the R atoms are H, Cl, Br, or mixtures thereof. The monomer itself may be used or a prepolymer of it may be used. Preferably, a prepolymer of about 50 to about 100 polymeric units is used as it has about the right combination of non-volatility and solubility. The compound or prepolymer is dissolved in a solvent such as xylene hexafluoride, the solution is applied to the article, and the solvent is evaporated.

EXAMPLE 1 Glass-epoxy test boards inches thick were provided with electrodes 6, /4 and /2 inches apart which passed .through the boards. Each group of 5 to 50 boards was placed in 100% relative humidity and tested periodically until the resistance between the electrodes no longer decreased. The tests were made at 500 volts after holding at 500 volts for one minute.

The first group of boards was cleaned with chlorethane then placed in 100% RH and tested. FIG. 2 gives the distribution of the resistances obtained for these boards.

The second group of boards was cleaned with chlorethane, then with isopropanol, rinsed with water, placed in 100% RH and tested. FIG. 3 gives the distribution of the resistances obtained with these boards and shows the considerable improvement which resulted from superior cleaning.

The third group of boards was cleaned as the second group, then was dipped into a 2% xylene hexafluoride solution of a prepolymer sold under the trademark PC- 706 by the 3M Company, believed to be a solution of C F Cl-I OOCC(CH )=CH The solvent was evaporated and the coating heated at C. for 10 minutes. The boards were placed in 100% RH and tested. FIG. 4 gives the distribution of the resistances obtained with these boards. In FIG. 4 the curve on the right is due to surface resistance and indicates that a large number of boards had no internal conductive paths. The smaller curve on the left is due to volume resistance and indicates that a small number of boards had internal conductive paths.

The fourth group of boards were made according to this invention. Glass cloth was dipped into a 0.2% aqueous solution of a surfactant sold under the trademark FC-95 by the 3M Company and analyzed as The solvent was evaporated leaving about 0.07% of the surfactant on the glass (based on the weight of the glass). The glass was coated with the same resin used to make groups one, two, and three-an epoxy resin (diglycidyl ether of bisphenol A), containing a hardener, catalyst,

tion was prepared which also did not contain the PC-- 134 but which used glass coated with a coupling agent 'y-aminopropyl trismethoxy silane. Then inch laminates were prepared as described in Example 1 and the copper surfaces etched to form electrodes about A: inch 5 particulate filler and dye. The resin also contained 0.02% apart stressing about 2 squares. The electrodes on each surfactant sold by the 3M Company under the trademark side were connected by drilled and plated holes. The PC-134, analyzed as following table gives the insulation resistance parallel 0 CH3 to the roving after various times at 95 to 100% RH, [CFPw FQ)T NH (CH2)S N:H] determined at 500 volts.

0 C 3 Resistance (ohms) after- The coated glass sheets were dried, stacked in groups of Laminate 1 day 2 days 6 days 8, then cured at 160 C. and 1500 p.s.i. for about an hour. Control 33x10, 13x10, 9X10, The resulting boards were cleaned as was the second group (goupling agentuu 1.5 10 12x10 of boards, then coated as was the third group of boards. F0434 6X1010 3.5 10 5X10 The boards were placed in 100% RH and tested. FIG. 5 gives the distribution of the resistances obtained with 3 above: table shows that after 6 days ,enough these boards. The curve on the left in 4 has 134 had migrated to the surfaces and resin-glass interappeared from FIG. 5 indicating that none of the boards 20 faces to cause a Increase inthe resistance. The coupling of this group had internal conducting paths. The boards W P ectwe m ralsmg the reslstance' were found to have a flexural strength of 75,000 p.s.i. in 1 1 the machine direction and 52,000 p.s.i. in the cross-dig g g g rection, a peel bond at 90 of 9 to 10lbs./in., a dielectric at r g f h d d constant at 4.9. after 96 hours at 35 C. in 90% RH, a z p F a 9; 70 a o ar ene syndissipation factor of 0.23 after 96 hours at 35 C. in 90% 2 g fi fg g 857 d fin RH, a dielectric strength (KV) of 90 to 100 in oil pari a allel to the laminate, and a water absorption of 0.11% after 24 hours at 23 C. in water. These properties are 2 apout 3; i g 9 i a i g comparable to the properties at identical boards not conavmg a P5 c 6 am at east 66 taming Surfactants bon atoms long at one end and a polar group EXAMPLE 2 at the other end, said surfactant possessing the property of lowering the surface energy of said Glass cloth of various finishes was dipped into a solu resin by freely migrating to the surface of said tron of varous surfactants. The cloth was then either an resin nd t it int face ith id fill fter dried or the surfactant was precipitated with hexane (see id resin i h d d; d Experiment No. 2 on following table). The cloth was (B) a conducting circuit bonded to at least one side dipped into a diglycldyl ether of bisphenol A resin conf id fl t b rd, wining an anhydride wring agent- Some resins also 2. An article according to Claim 1 wherein said resin tained a surfactant. The cloth was heated to B-stage 40 i n epoxy resin and said filler is glass fibers. the resm thereby forming sheets. Eight sheets were stacked 3, A ti l according t Cl i 1 h r i s id surwith 1 oz. copper foil at each face and pressed at 1500 factant has the general formula p.s.i. for about an hour at 160 C. to form boards. F X Y Electrodes were etched on the copper surfaces and were C11 2m connected face-to-face by drilled and plated holes. After where each X is independently selected from the group storage at 95 to 100% RH for various lengths of time, consisting of F, H, Cl, Br, and mixtures thereof, Y is the average insulation resistance was determined at 500 a polar group capable of being chemisorbed onto said volts. The following table gives the results: filler, m+n is an integer from 3 to 18, and ml is an in- Resistance (ohms) after- Experi- Surfactant solution Surfactant ment No. Finish on cloth deposited on cloth in resin 1 day 3 days 5 days 15 days 1 H at cleaner] 0.1% FC95in methanol 0.01% EC-95"--. 5x10 1.4 10 4X10 (in 0.2% FC-95precepitated None 1.s 10 113x10 1.o 10 1.3)(10 a do 02% EC-95" in water d0 1.7 1o 1.6 1o 2.0x10 4 do 0.2% C FmO0OH in water 0 5 10 1.3)(10 5 Glyeidoxytrismethoxy silane 0.2% CxsFuCOOH in Water. 7X10 6 Heat cleaned 0.2% MP D-3676" in water 2x10 5x10 7 do 0.2% TO-134 in water.--" 2x10 1.5 10 8 An 0.1% CnF COOH in water 2.4X1012 n (in 0.2% "EC-134" in water do 3x10 1.6x 9 (control) dn Nonedo 9x10 4x10 2.5 10= 25x10 MPD-3676 is a trademark of the Du Pont Company 0 and is analyzed as having the structure second identical composition was prepared which did not contain the PC-134, and a third and fourth compositeger at least as great as the truncated product of 0.2

times n.

4. An article according to Claim 3' wherein n+m is an integer from 6 to 12.

5. An article according to Claim 3 wherein Y is where each R is independently selected from the group consisting of hydrogen and alkyl to C R is alkylene from C to C R is alkyl to C and A- is an anion.

6. An article according to Claim 1 wherein said surfactant is concentrated on said filler and has the general formula n 2n+1 m 2m where each X is independently selected from the group consisting of F, H, Cl, Br, and mixtures thereof, Y is a polar group which resists chemisorption on said filler, m-+n is an integer from 3 to 18, and m is an integer at least as great as the truncated product of 0.2 times n. 7. An article according to Claim 6 wherein n+m is an integer from 6 to 10.

8. An article according to Claim 6 wherein Y is selected from the group consisting of -coon, -so,H, -0PO(OH)(OM),

and salts thereof, where M is selected from the group consisting of H and -C X C F where m+n is an integer from 3 to 18, m is an integer at least as great as the truncated product of 0.2 times 1:, and each X is independently selected from the group consisting of F, H, Cl, Br, and mixtures thereof.

9. An article according to Claim 8 wherein said surfactant iS C7F15CO0H.

8 v References Cited UNITED STATES PATENTS 3,741,858 6/1973 Fujiwara 161-186 3,388,036 6/1968 Alanpi 161-186 3,678,068 7/1972 Anello 252-351 3,649,583 3/1972 Gunthrie 260-37 EP 3,458,571 7/1969 Tokoli 260-556 3,450,755 7/1969 Ahlbrecht 260-556 3,478,116 11/1969 Smeltz 260-633 3,342,875 9/1967 Selman 260-615 3,094,547 6/1963 Heine 260-461 OTHER REFERENCES Bernett, Wetting Acid & Salts, I. of Phys. Chem, vol. 63, pp. 1911-16 (November 1959).

LEON D. ROSDOL, Primary Examiner M. F. ESPOSITO, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,8 ll,957 Date-d October- 1 3 M711 Inv nt Gerhard R. Snrenszlinsr It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 19, after "-80 H" insert OPO(OH)(OM),

Signed and Scaled this ninth Day of September 1975 [SEAL] A ttest:

RUTH C. MASON C. MARSHALL DANN A HXII'HK Offi (mnmisxivm'r ujlarenrs and Trademarks 

1. AN ARTICLE COMPRISING (A) A FLAT BOARD WHICH COMPRISES (1) ABOUT 15 TO ABOUT 70% OF A HARDENED, SYNTHETIC, ORGANIC RESIN; (2) ABOUT 30 TO ABOUT 85% NON-CONDUCTIVE FILLER; AND (3) ABOUT 0.001 TO ABOUT 1.0% OF A SURFACTANT HAVING A PERFLUORINATED CHAIN AT LEAST THREE CARBON ATOMS ALONG AT ONE END AND A POLAR GROUP AT THE OTHER END, SAID SURFACTANT POSSESSING THE PROPERTY OF LOWERING THE SURFACE ENERGY OF SAID RESIN BY FREELY MIGRATING TO THE SURFACE OF SAID RESIN AND TO ITS INTERFACES WITH SAID FILLER AFTER SAID RESIN IS HARDENED; AND (B) A CONDUCTING CIRCUIT BONDED TO AT LEAST ONE SIDE OF SAID FLAT BOARD. 